Weather

750 
fxus66 ksgx 102028 
afdsgx 


Area forecast discussion 
National Weather Service San Diego California 
200 PM PDT Friday Oct 10 2008 


Synopsis...a strong low pressure trough will bring strong winds to 
the mountains and deserts...as well as a slight chance of showers 
except in the deserts. It will also bring very cool weather Saturday 
with the passage of a cold front. Offshore flow will develop on 
Sunday producing a warming trend and Santa Ana wind conditions. The 
strongest northeast winds will occur Monday morning through and 
below mountain passes...then will weaken Tuesday. 


&& 


Discussion...for extreme southwestern California including Orange... 
San Diego...western Riverside and southwestern San Bernardino 
counties... 


The partial clearing pattern is slow and some clouds will continue 
over the area except the deserts tonight into early Sat. A cold 
front passing through the region could produce a few showers. The 
deep upper trough is on schedule to drop down into socal tonight. 
Strong winds will get stronger this evening in the mountains and 
deserts and a Wind Advisory is in effect. The winds combined with 
the low humidity in the upper desert is the reason for the short 
window red flag warning there until 8 PM this evening. 
The cold front associated with this deep upper trough will move 
through the residual marine layer moisture and what tiny amount of 
moisture is aloft...a few showers could be squeezed out most likely 
in the coastal mountain slopes...but still remotely possible 
anywhere west of the mountain crests. The best chance of this is 
between around 9 PM tonight and 6 am Sat. The winds drop off Sat and 
the big story will be simply the coolest weather since March or so. 
On Sat night and sun the flow gradually turns northerly then 
northeast. This will dry out the air all the way to the coast. The 
offshore flow increases a lot Sun night and Monday morning to add 
strong winds to that dry air...to the tune of 20 to 40 miles per hour sustained 
winds in the foothills and below passes...with peak winds topping 60 
miles per hour. Obviously the fire growth potential GOES way up. Although this 
upcoming Santa Ana event will be serious...it appears weaker in all 
respects than the Oct 2007 event. Wind speeds and durations will be 
less and temperatures will be lower. Winds will decrease Monday night and then 
especially Tuesday afternoon...but the humidity will continue very low 
through Wednesday. A warming trend will start sun and continue through Thursday 
as high pressure develops aloft. 


&& 


Aviation... 
101900z...marine layer depth this afternoon is close to 5000 feet. 
Marine depth should remain near 5000 feet through tonight before 
lowering on Saturday behind a cold front expected to pass through 
between 12z and 15z. Layers of broken stratocu with bases ranging 
between 2500 and 4500 feet will remain over the area through tonight 
up against the coastal slopes of the mountains with mountains and 
higher terrain obscured at times. Stratocu should break up rapidly 
on Saturday behind the front as the flow aloft becomes more 
northwest to north. 


Above the marine layer...a mostly clear sky with unrestricted 
visibilities will continue through Saturday. 


Gusty west to northwest winds across the mountains this afternoon 
and tonight will bring some mountain wave and rotor activity with 
associated up and down drafts and low level wind shear to the desert 
areas around kpsp and ktrm. This could also result in areas of 
blowing dust and sand near these airports. 


Saturday night and Sunday the flow aloft becomes more northerly 
which should bring some mountain wave/rotor activity south of the 
San Bernardino and san gabiel mountain range resulting in up and 
down drafts and low level wind shear in the vicinity of kont. Horton 


&& 


Fire weather... 
strong winds and low humidities of 15-20 percent persist in the high 
deserts this afternoon. Expect humidities to remain below 15 percent 
this afternoon and and recover into the 20 to 30 percent range. 
Winds will continue at 20 to 30 miles per hour with gusts to 40 miles per hour. Red flag 
warning remains in effect until 8 PM. 


Humidities from 15 to 20 percent Sunday morning will fall into the 
single digits in the afternoon. Santa Ana event developing Sunday 
night and Monday with NE winds of 20 to 40 miles per hour in many areas with 
gusts to 50 miles per hour or more through the passes and canyons. Winds will 
weaken Tuesday afternoon...but dry conditions will persist into 
Wednesday. 


&& 


Sgx watches/warnings/advisories... 
Wind Advisory through 9 am Saturday morning for the mountains and 
deserts...see laxnpwsgx. 


Red flag warning until 8 PM PDT today for the apple and Lucerne 
valleys...see laxrfwsgx. 


Small Craft Advisory for the outer waters 5 PM this afternoon 
through 11 am Saturday...see laxmwwsgx. 


&& 


$$ 


Public...mm 
aviation/marine...Horton 
fire weather...pg